I can confirm that that is a good idea, err, to NOT drop it in the sea I mean. Also do not sit down in surf, however accidentally, with one in your pocket.
Have youse folk not heard of waterproof cases
for mobile phones? Since I got one of those I haven't fallen in the water at all.
Oh, yes, of course I have one of those. It ws in the side pocket of my bag on the boat at the time.
But I do like your assessment of it's magic powers. I expect it will also keep the elephants away. My magic umbrella works in the same way, it only rains when I don't carry it with me.